As semiconductor devices continue to decrease in size and more and more applications have been found for the micro and nano-devices, there is an urgent need for measuring physical quantities at sub-micrometer or even nanometer size dimension. Temperature is one of the fundamental physical quantities that routinely needs to be measured in order to derive other thermodynamic quantities such as heat, energy, or specific heat capacity.
Presently temperature can be measured using a thermocouple, a semiconductor diode, a metallic resistor, a thermister, an infrared thermometry, a near-field thermometry, and other more exotic methods. Each technique has its own advantages and disadvantages. For example, the thermocouple is extremely simple in design and inexpensive, while the semiconductor diode is not suitable for high temperature but used extensively to measure cryogenic temperature. The spatial resolution of most of the above techniques is about 10 microns, except for the near field thermometry in which the spatial resolution can be in the order of 50 nm. But near field thermometry involves complicated optical instrumentation and is very cumbersome. There are several efforts to improve the spatial resolution of temperature measurements by combining scanning tunneling microscopy (STM) or atomic force microscopy (AFM) with a small thermocouple or thermistor tip. U.S. Pat. No. 5,581,083 to Majumdar et al, described a method of fabricating nanometer hole on the tip of a scanning probe. The size of the holes define the area of interaction of the sensor with the environment. In U.S. Pat. No. 5,838,005, Majumdar et al extended the above patent to include using focus ion beam for fabricating the nano scale holes. However, it should be noted that the size of their sensors is still limited by the lithographic technique used. In addition, thermoelectricity of certain bulk materials drop drastically due to the constricted geometry of the AFM tip arrangement.
It would be very important to develop a much smaller sensor and a process by which the size of said sensor can be controlled to a nano size as small as 50 nm.